An optical communication system has been promoted to be large in communication capacity and to have as many highly advanced functions as possible. On the other hand, an optical fiber network system has been required to be small in size, low in cost, and high in integration degree. Among these tendencies, it will inevitable that an optical device such as an optical transmitter, an optical receiver, etc. is required to be small in size, low in cost, and high in integration degree. In various optical devices now used practically, a spatial connection using a lens, etc. defined "microoptics" is used to connect an optical fiber to optical parts such as a semiconductor light source, an optical semiconductor detector, an optical demultiplexer, etc. The microoptics structure is difficult to be small in size, because there is limitation in size in regards to the configuration of a lens; and packages for semiconductor light source, an optical semiconductor detector, and so on. In order to effectively couple a light propagating through air space to an optical fiber and an optical detector, it is required to adjust the axial alignment of light with high precision. In this adjustment of the light axial alignment, much labor is required to be high in cost. For this reason, the microoptics structure is not appropriate to be used for high integration of devices having the same and different functions.
In these days, the necessity of optical bidirectional communication systems has been increased, and it has ben required that these systems are introduced into individual homes. In such an optical bidirectional communication system, an optical transmitter and an optical receiver are used. If such optical devices are used as discrete parts, an optical transmission and receiving apparatus becomes large in size to hinder the propagation of these systems.
In such a situation, a proposal in which an optical waveguide is used for the purpose of small size, high integration, and low cost in place of the microoptics structure is described on pages 1530 to 1539 of "IEEE Lightwave technology, 1989".
One type of an optical device using optical waveguides comprises an optical multiplexer and demultiplexer formed on a substrate. In the optical device, the optical multiplexer and demultiplexer is connected via optical waveguides to a semiconductor light source and semiconductor photodetectors which are also mounted on the substrate, and the semiconductor light detectors are connected via electric interconnections to electronic semiconductor devices. Further, one or some of the optical waveguides are directly coupled to an optical fiber for propagating lights between the optical device and another optical device.
In the optical device, the light source emits a light modulated by a transmitting signal, and the light is supplied via the optical multiplexer and demultiplexer to the optical fiber, through which the light is transmitted to the other optical device. On the other hand, the optical multiplexer and demultiplexer receives a light transmitted from the other optical device by the optical fiber, and demultiplexes the light to be supplied to the optical detectors, from which electric signals are supplied to the electronic devices. Thus, the processing of the electric signals are carried out.
In the optical device, however, there is a disadvantage in that an optical coupling of high efficiency between of the optical parts and a corresponding one of the optical waveguides is difficult to be obtained, because the light axial alignment is required to be adjusted with a precision of approximately l.mu.m in the three dimensional (X, Y and Z) directions.